This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-25193 filed Feb. 2, 2000.
The present invention relates generally to a clutch and, more particularly, to a clutch that prevents transmission of a rotational force from its driven side to its driving side and also a motor having such a clutch.
PCT publication No. WO00/08349 published on Feb. 17, 2000 proposes a clutch that prevents transmission of a rotational force from the driven side to the driving side.
This clutch includes an outer ring, a driving-side rotator, a driven-side rotator and rolling elements. The driving-side rotator is rotatably received within the outer ring and is connected to a drive source. The driving-side rotator includes engaging slots having an opening on its outer circumferential side (inner circumferential side of the outer ring).
The driven-side rotator is rotatably received within the outer ring and is connected to a load. The driven-side rotator has engaging projections for rotatably engaging with the corresponding engaging slot of the driving-side rotator. A control surface opposing an inner circumferential surface of the outer ring is provided on an outer circumferential surface of each engaging projection.
Within the opening of each engaging slot, the corresponding rolling element is positioned between the inner circumferential surface of the outer ring and the control surface. The rolling element has a diameter that is smaller than a distance between a circumferential center portion of the control surface and the inner circumferential surface of the outer ring but is longer than a distance between each of opposing circumferential end portions of the control surface and the inner circumferential surface of the outer ring.
In this clutch, when the driving-side rotator is rotated, each rolling element is urged by an inner wall surface of the opening of the corresponding engaging slot and is substantially positioned in the center portion of the control surface. The rotational force of the driving-side rotator is conducted from each engaging slot to the driven-side rotator via the corresponding engaging projection.
When the driven-side rotator is rotated, each rolling element is urged by the control surface against the inner circumferential surface of the outer ring and is clamped between the inner circumferential surface of the outer ring and the control surface to prevent rotation of the driven-side rotator.
The control surface of the above-described clutch should be formed such that a distance between the control surface and the outer ring decreases from the circumferential center portion toward the opposing circumferential end portions. In the above-described clutch, the center portion of the control surface is located radially inward (closer to the rotational center) of a straight line connecting the opposing circumferential end portions, and part of the control surface between the center portion and each one of the circumferential end portions is flat. Alternatively, the entire control surface may be in a single flat surface.
In the above-described clutch, it is difficult to make a small radial gap between the rolling element and the opposing circumferential center portion of the control surface as well as between the rolling element and the opposing inner circumferential surface of the outer ring. If these gaps are further reduced, a slight movement of the rolling element out of the center portion causes the rolling element to be clamped between the control surface and the inner circumferential surface of the outer ring. Furthermore, when the driving-side rotator is rotated, the rolling element may not be accurately positioned in the center portion, so that the rotation of the driving-side rotator may be prevented. On the other hand, if these gaps are further increased, the rolling element is allowed to move substantially in a radial direction when the driving-side rotator is rotated. This radial movement of the rolling element causes generation of noises.
Also, in the above-described clutch, when the rolling element is urged by the circumferential end portion of the control surface against the inner circumferential surface of the outer ring, a radially outwardly directed force component of the urging force exerted by the circumferential end portion cannot be sufficiently increased. Thus, when the driven-side rotator is rotated, the rolling element may not be clamped between the control surface and the inner circumferential surface of the outer ring. That is, the rolling element may move along the inner circumferential surface of the outer ring.
Thus, it is an objective of the present invention to provide a clutch having a reduced noise level as well as a motor having such a clutch.
It is another objective of the present invention to provide a clutch which is capable of preventing transmission of a rotational force from its driven-side to its driving-side as well as a motor having such a clutch.
To achieve the objective of the present invention, there is provided a clutch including an outer ring, a driving-side rotator, a driven-side rotator and a rolling element. The outer ring is non-rotatably secured and has an inner circumferential surface. The driving-side rotator is connected to a drive source and is rotatably received within the outer ring. The driving-side rotator includes an engaging slot that has an opening at its outer circumferential side. The driven-side rotator is connected to a load and is rotatably received within the outer ring. The driven-side rotator includes an engaging projection, which engages the engaging slot to limit relative rotation of the driving-side rotator within a predetermined range and which has a control surface opposing the inner circumferential surface of the outer ring at its outer circumferential wall surface.
The rolling element is located between the inner circumferential surface of the outer ring and the control surface in the opening and that has a diameter shorter than a distance between a circumferential center portion of the control surface and the inner circumferential surface of the outer ring but longer than a distance between each of opposing circumferential end portions of the control surface and the inner circumferential surface of the outer ring. Specifically, the circumferential center portion of the control surface is located radially outward of a straight line that connects the opposing circumferential end portions of the control surface. Each intermediate portion positioned between the circumferential center portion and a respective one of the circumferential end portions is arcuately bulged in a radially outward direction beyond a corresponding straight line that connects the circumferential center portion and a corresponding one of the circumferential end portions.
Furthermore, to achieve the objective of the present invention, there is also provided a motor having the above-described clutch.